and for the very latest on the investigation, we're joined now by nbc news justice correspondent pete williams from washington. so, pete, the very latest on the pressure cooker scenario that you're hearing? >> right. as you say, used for decades in terms of building bombs, so that's not going to be an area of inquiry that will immediately lead them in a certain direction, because the instructions, unfortunately, for making these devices are all over internet. just last month, the al qaeda online magazine "inspire" repeated an article that showed how to build pressure cooker bombs. so they've been out there for a long time. the part, the components of this device appear not to be very fancy. in addition to that, there were shrapnel, ball bearings, bbs, from the sound of the doctors you heard at the beginning of your program, apparently nails as well. and then for the explosive basically gun powder, smokeless powder that's commonly available in sporting goods stores. so all these pieces are easily available. some kind of timer as well. then placed in black sacks and put in two different